The basic nature of the force, duration and frequency of tooth contacts during bruxing and mastication will be investigated. The changes in nocturnal and daytime bruxing habits with modification in occlusion will be measured. Time dependencies among jaw movement, EMG activity and tooth force will be documented. Forces recorded during bruxing will be compared with forces recorded during chewing to evaluate the potential damage to the periodontium of bruxism in relation to mastication. A system for measuring the jaw force will be developed as the first part of this project. This system will deduce jaw force from measurements of the variations in amplitude of introduced vibrations which are transmitted by the facial bones, periodontium and teeth. This system avoids using mouth appliances which could interfere with and change the preconscious function. Also, this vibration transmission system will be evaluated for use in measuring tooth mobility.